Aircraft wing to fuselage joints need to be lightweight and low cost to produce and maintain. Increasingly in the current aircraft industry, the time to assemble such joints is also a key driver, as manufacturers face the challenge of greater production rates to meet demand. Specifically, the time to assemble large aircraft assemblies (e.g. wing to fuselage) is of financial interest, due to the large cost of the work in progress locking in cash to the business at the final assembly line.
Most large aircraft have a two-spar wing box structure, and the wing-fuselage joint connects the centre wing box structure on the fuselage side to the wing box structure on the wing side. Of course, two such joints are provided, one on each side of the fuselage. The wing-fuselage joint typically comprises a series of joints around the circumference of the wing box structure. On the fuselage side, the joint typically connects to upper and lower tri-form, or cruciform, components and to front and rear spars of the centre wing box structure. On the wing side, the joint typically connects to upper and lower wing covers, and to front and rear wing spars of the wing box structure.
Traditionally, weight-optimised wing-fuselage joint designs focus on shear joints, where surfaces of components are overlapped and then bolted together; or tension joints, where surfaces of components are butted together and secured with tension bolts (often via a bracket). Typically, tension joints are heavier than their shear-joint equivalents due to the inefficient way that load is transferred. However, shear joints typically take longer to assemble than tension equivalents due to the large number of bolts required and the accuracy required in matching the positions of overlapping surfaces around the joint perimeter. Currently, it takes around 50-100 hours to form a wing-fuselage joint for a medium/large aircraft by forming shear joints in composite structures.